Ultrasonic diagnostic equipment has become an indispensable tool for clinical use. For approximately the past twenty years, real-time B-mode ultrasound imagers are used for investigating all soft tissue structures in the human body. One of the recent developments within medical imaging technology is the development of Doppler ultrasound scanners. Doppler ultrasound is an important technique for non-invasively detecting and measuring the velocity of moving structures, and particularly to display an estimate of blood velocity in the body in real time.
The basis of Doppler ultrasonography is the fact that reflected and/or scattered ultrasonic waves from a moving interface undergoes a frequency shift. In general the magnitude and the direction of this shift provides information regarding the motion of this interface. How much the frequency is changed depends upon how fast the object or moving interface is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.
There are several forms of depiction of blood flow in medical Doppler imaging or more generally different velocity estimation systems that currently exist: Color Flow imaging, power Doppler and Spectral sonogram. Color flow imaging (CFI), interrogates a whole region of the body, and displays a real-time image of mean velocity distribution. CFI provides an estimate of the mean velocity of flow with a vessel by color coding the information and displaying it, super positioned on a dynamic B-mode image or black and white image of anatomic structure. In order to differentiate flow direction, different colors are used to indicate velocity toward and away from the transducer.
While color flow imaging displays the mean or standard deviation of the velocity of reflectors, such as the blood cells in a given region, power Doppler (PD) displays a measurement of the amount of moving reflectors in the area, similarly to the B-mode image's display of the total amount of reflectors. A power Doppler image is an energy image in which the energy of the flow signal is displayed. Thus, power Doppler depicts the amplitude or power of the Doppler signals rather than the frequency shift. This allows detection of a larger range of Doppler shifts and thus better visualization of small vessels. These images give no velocity information, but only show the direction of flow. In contrast, spectral Doppler or spectral sonogram utilizes a pulsed wave system to interrogate a single range gate or sampling volume, and displays the velocity distribution as a function of time. The sonogram can be combined with the B-mode image to yield a duplex image. Typically, the top side displays a B-mode image of the region under investigation, and the bottom displays the sonogram. Similarly, the sonogram can also be combined with the CFI or PD image to yield a triplex image. The time for data acquisition is then divided between acquiring all three sets of data, and the frame rate of the images is typically decreased, compared to either CFI or duplex imaging.
The current ultrasound systems require extensive complex data processing circuitry in order to perform the imaging functions described herein. Doppler processing for providing two-dimensional depth and Doppler information in color flow images, power Doppler images and/or spectral sonograms require millions of operations per second. There exists a need for an ultrasound imaging system that provides for compute-intensive systems and methods to efficiently address the data processing needs of information, such as Doppler processing.